1. Field of the Invention
This invention relates generally to improvements in mechanical oscillators or traverse mechanisms, and more particularly to improvements in the reciprocator illustrated and described in U.S. Pat. No. 3,792,616 entitled RECIPROCATING DRIVE, having common ownership with the present application.
The entire disclosure of U.S. Pat. No. 3,792,616 is specifically incorporated herein, by reference.
2. Description of the Related Art Including Information disclosed under 37 CFR Sections 1.97-1.99
The following patents are hereby made of record, as being related to the field to which the present invention pertains:
______________________________________ U.S. Pat. Nos.: ______________________________________ 2,258,114 3,296,880 3,308,674 3,648,535 3,766,788 3,766,800 3,779,094 3,803,926 3,844,177 4,008,625 4,022,076 4,031,765 4,198,872 4,199,999 4,274,296 4,343,200 4,693,131 4,730,503 5,191,805 British Patent No. 1044 dated Jan. 15, 1907 French Patent No. 526,586 ______________________________________
U.S. Pat. No. 3,792,616 above identified discloses a mechanical oscillator comprising a turnable shaft having two parallel, endless tracks or grooves of loop-like configuration, and a nut body carrying radially-disposed rollers on bearings. The path of each track generally defines an ellipse. The rollers each have a nose which engages the walls of the respective grooves as the shaft is turned, such that the nut undergoes reciprocating movement as the shaft is driven. Centralizers in the form of needle bearings are provided at opposite ends of the nut body, to maintain the alignment between the axis of the latter and that of the shaft.
The patented construction has enjoyed a degree of commercial success, and has been found to operate satisfactorily for certain specific applications.
However at high speeds, problems are encountered with roller slippage and excessive wear, even with appropriate lubrication of the relatively moveable parts. In particular, with such arrangements the inertia of the nut body during reversal, must be overcome at each end of the reciprocating stroke, causing relatively large (though momentary) forces to be applied to the individual rollers and their respective bearings at the points of reversal.
In addition, more serious is the problem of slippage of the individual rollers on the walls of the tracks as reversal is occurring. In particular, with the disclosed construction, both rollers tend to turn in one direction about their respective axes for one-half of the reciprocating cycle, and then, by virtue of their shift to engagement with the opposite faces or walls of the grooves, each roller is suddenly subjected to a force which tends to cause it to suddenly reverse its direction of turning.
As can be readily appreciated, in practice, sudden or instantaneous reversal of the direction of turning of the individual rollers does not readily occur. Instead, there arises some combination of sliding of the individual rollers against the opposing groove wall, followed by eventual reversal of the direction of rotation, assuming that the speeds involved are sufficiently slow to permit the inertia of the rollers to be overcome at all. As a consequence, excessive wear occurs, and the anti-friction characteristic of the oscillator, as intended by the provision of the anti-friction bearings for each roller, is seen to be largely lost, or at best, significantly diminished.
An early use of thread-engaging rollers in a helical-type screw is disclosed in British Patent No. 1044 issued in January, 1907, and French Patent No. 526,586 issued in October, 1921.
Refinements in the constructions noted in the previous paragraph appear in U.S. Pat. Nos. 3,296,880; 3,308,674; 3,648,535; and 4,274,296. In these patents there is disclosed a number of anti-friction mechanical drive constructions involving Acme-type helical thread forms, and nut structures comprising various type of anti-friction rollers, and including bearings for the rollers. Several of the disclosed constructions have enjoyed considerable commercial success over the years.
Various improvements to some of these patented structures have been devised. In particular, in U.S. Pat. No. 3,766,788, anti-friction rollers are housed in bushing assemblages which have outer cylindrical walls that are eccentric with respect to the respective roller housed therein. The arrangement is such that each bushing can be adjustably turned in its respective radial socket in the nut body, so as to effect a lateral shifting of the roller. This enables the user to accommodate slight variations in thread pitch which are encountered during normal manufacturing operations involved in fabrication of the screw.
Another arrangement is shown in U.S. Pat. No. 3,766,800, which features a nut/screw combination having anti-friction rollers, wherein the nut, in addition to the thread-engaging rollers, has conventional internal threads which are purposely made. undersize, and which do not normally engage the screw threads unless an unusually high axial load is applied between the nut and screw. Under such high loads, the rollers become retracted to the extent that the fixed thread form of the nut engages the screw, thereby to alleviate excessive loading on the rollers, and to prevent a catastrophic failure of the nut/screw which otherwise might result.
Still other variations on the patented devices noted above are illustrated in U.S. Pat. Nos. 4,008,625; 4,198,872; 4,199,999; and 5,191,805. In U.S. Pat. No. '625, two nut components or parts are cascaded along a screw, each component having a radial roller which is spring biased into engagement with a wall of the thread groove. A coil spring carried by one of the nut parts, in turn applies an additional spring bias to the nut components so as to cause the roller of one component to "hug" one wall of the thread groove, and the roller of the other component to "hug" the opposite wall of the groove, thereby to minimize backlash of the cascaded nut assembly.
U.S. Pat. No. 4,198,872 discloses a modified anti-friction nut adapted for relatively light loads, and with a more conventional helical thread form. In place of anti-friction rollers, the disclosed construction utilizes balls as the thread-engaging elements. Slippage of the balls on the thread occurs as the screw is turned. Each ball is carried in a radially-extending socket constituted as a bushing having a cup-shaped ball seat.
An improvement in the construction of U.S. Pat. No. 4,198,872 above identified is shown in U.S. Pat. No. 4,199,999. This latter device incorporates a special cage and housing in order to hold captive a series of thread-engaging balls. The cage and housing telescope with one another, and the resultant structure was found to be more economical to manufacture than some of the prior anti-friction drives of the type utilizing balls as anti-friction elements.
A further simplified anti-friction drive for a screw having a modified Acme thread is illustrated in U.S. Pat. No. 5,191,805. A radial roller is provided on a nut body, supported on inner and outer ball bearings. The use of ball bearings has been found to be especially economical, since their cost is quite low, and they are readily available in the marketplace and at very competitive prices.
Modified structures employing anti-friction rollers are shown in U.S. Pat. No. 3,779,094, which utilize a diamond-thread screw in place of a helical-thread type screw. Special roller cartridges are arranged to be slidable on the nut body, thereby permitting lateral shifting of selected rollers, which results in the capability of reversal of the nut at either one of the opposite ends of the screw thread, or at selected points along the screw, namely at the location of the groove intersections of the diamond thread.
Other anti-friction constructions illustrating the use of balls as thread-engaging elements are shown in U.S. Pat. Nos. 4,022,076 and 4,031,765. In U.S. Pat. No. '076, there is illustrated an anti-backlash mechanism to reduce looseness between a nut and screw. U.S. Pat. No. '765 constitutes an improvement in U.S. Pat. No. 3,779,094, in that the use of rollers has been eliminated, and thread engaging balls employed to engage the screw, while still maintaining the capability of reversal of the nut at the ends of the screw thread.
U.S. Pat. No. 4,343,200 illustrates a reversing mechanism employing a diamond thread screw, and a special reversing collar that can be selectively applied to the diamond thread at various points therealong, so as to enable the direction of travel of the nut to be reversed at any one of a plurality of points along the thread. The collar in effect, provides a selectively installable and removable abutment or "reversing groove" at any one of a number of different points along the length of the screw.
Somewhat different arrangements for providing reciprocating drives are illustrated in U.S. Pat. Nos. 3,803,926 and 4,693,131. Both of the disclosed devices utilize what is known in the industry as "ball screws". U.S. Pat. No. '926 involves a drive shaft having oppositely-threaded portions, i.e. both left- and right-hand threads, whereas U.S. Pat. No. '131 involves a ball screw for positioning a worktable, the mechanism utilizing two stepping motors that are arranged to be selectively either additive or differential as to the speed at which the table is driven.
Other reciprocating systems employing oppositely-threaded sections of a turnable drive shaft are disclosed in U.S. Pat. Nos. 3,844,177 and 4,730,503.
Finally, U.S. Pat. No. 2,258,114 discloses a box cam arrangement utilizing a bearing-mounted roller on a reciprocating carriage, and wherein the drive cam is provided with a spring mounting that tends to absorb impulse-type forces which would otherwise be transmitted to the cam follower portion of the box cam.
In the case of the anti-friction drive constructions noted above and of the type which employ either a simple helical thread or a diamond thread, the problem of sudden reversal in the axial movement of a nut was not generally addressed. In most of the other patented devices discussed above, reversal occurs typically at relatively low operational speeds.
Thus, the problem of inertia of the nut body at the point of reversal remains unsolved, to a large extent. Also, the problem of inertia of a roller element giving rise to wear of either the roller or the thread surface, has not been adequately discussed in the prior art noted above.
Where high speed operation is required and where there arises the need to suddenly reverse the direction of rotation of a roller in order to minimize sliding contact between it and a thread groove wall, the matter of impulse-type torque or forces applied to the individual rollers must be considered. Where a non-sliding contact cannot be realizeable for reasons of excess speed, or high load, there occurs excessive wear, which more often than not, proves to be intolerable; in addition, where sliding of a roller occurs, the resulting friction not only defeats the anti-friction characteristic of the mechanism, but in addition, creates heat.
As a consequence, there has arisen a need for a high-speed, relatively long-life oscillator mechanism which will resist wear and operate in a satisfactory manner over prolonged time periods. In addition, there has arisen a need for an oscillator construction which can be easily serviced, and where replacement of parts on a routine basis, somewhat analogous to periodic maintenance, can be realized.